This invention relates to a method of reducing particulate emissions from the exhausts of internal combustion engines powered by diesel fuels.
Of particular interest are fuels such as diesel which are used widely in automotive transport and for providing power for heavy duty equipment due to their high fuel economy. However, one of the problems when such fuels are burned in internal combustion engines is the pollutants in the exhaust gases that are emitted into the environment. For instance, some of the most common pollutants in diesel exhausts are nitric oxide and nitrogen dioxide (hereafter abbreviated as xe2x80x9cNOxxe2x80x9d), hydrocarbons and sulphur dioxide, and to a lesser extent carbon monoxide. In addition, diesel powered engines also generate a significant amount of particulate emissions which include inter alia soot, adsorbed hydrocarbons and sulphates, which are usually formed due to the incomplete combustion of the fuel and are hence the cause of dense black smoke emitted by such engines through the exhaust. The oxides of sulphur have recently been reduced considerably by refining the fuel, e.g., by hydrodesulphurization thereby reducing the sulphur levels in the fuel itself and hence in the exhaust emissions. However, the presence of particulate matter in such exhaust emissions has been a more complex problem. It is known that the primary cause of the particulate matter emission is incomplete combustion of the fuel and to this end attempts have been made to introduce into the fuel organic compounds which have oxygen value therein (hereafter referred to as xe2x80x9coxygenatesxe2x80x9d) to facilitate combustion. Oxygenates are known to facilitate the combustion of fuel to reduce the particulate matter. Examples of such compounds include some of the lower aliphatic esters such as, e.g., the ortho esters of formic and acetic acid, ethers, glycols, polyoxyalkylene glycols, ethers and esters of glycerol, and carbonic acid esters. For instance, U.S. Pat. No. 5,308,365 describes the use of ether derivatives of glycerol which reduce particulate emissions when added to diesel fuel. This patent teaches that the amount of reduction in particulate matter is linearly proportional to the oxygen content of the added components, i.e., the greater the oxygen content the higher are the reductions in particulate matter for a range of added compounds and that it is independent of the specific compound chosen over the range described.
Similarly, Society of Automotive Engineering paper 932734 summarizes a heavy-duty diesel engine study over a broader range of oxygenated fuels and one of the authors (Liotta, F J) is also one of the inventors of U.S. Pat. No. 5,425,790 (alcohols and glycols) and U.S. Pat. No. 5,308,365 (glycerol ethers and esters). The authors confirm that the amount of reduction in particulate matter scales roughly linearly with the oxygen content of the component added although ethers seem to be more effective for reducing particulates than alcohols for the same oxygen content.
Again, SAE Paper No. 942023 teaches the use of alcohols generically disclosed as A and B. This paper however fails to identify the alcohols tested.
Similarly, U.S. Pat. No. 5,425,790 (corresponding to SAE 932734) discloses the use of cyclohexyl ethanol and methyl benzyl alcohol as additives for fuels to reduce particulate emissions and states that these do not work (col. 6, lines 53-57). No other alcohols are disclosed. This reference which is primarily concerned with testing glycols and glycol ethers, does not state in what concentration the alcohols were tested.
U.S. Pat. No. 4,378,973 discloses the use of a combination of cyclohexane and an oxygenated additive for reducing particulate emissions from fuels. This document states that the beneficial effect cannot be achieved in the absence of cyclohexane. This document discloses 2-ethyl hexanol and xe2x80x9cEPAL 1012xe2x80x9d which comprises a mixture of normal C6-C20 alcohols as the oxygenated additives.
A further reference, WO 93/24593, is primarily concerned with gasohol blends from diesel and alcohols. This blend must contain 20-70% by volume of ethanol or methanol, 1-15% by volume of a tertiary alkyl peroxide and 4.5-5.5% by volume of a higher straight chain alcohol. The straight chain alcohols disclosed have from 3-12 carbon atoms. According to this reference the presence of a tertiary alkyl peroxide is essential for the performance of the fuel since using 10% v/v alcohol performs no better than a straight diesel whereas 30% v/v of ethanol xe2x80x9cseverely degraded the engine""s operationxe2x80x9d (page 8, lines 14-19).
WO 98/35000 relates to lubricity enhancing agents and makes no mention of controlling or reducing emission of particulate matter. This document discloses the use of primary, linear C7+alcohols in an amount of  less than 5% w/w of a diesel fuel composition.
Similarly, WO 96/23855 relates to the use of glycol ethers and esters as lubricity enhancing additives to fuel oils such as diesel. There is no mention of using any alcohols as such although several alcohols have been listed as being used to prepare the ethers and esters.
Like the WO 96/23855 above, U.S. Pat. No. 5,004,478 refers to the use of polyethers and esters of aromatic carboxylic acids in diesel fuels as additives. There is no mention of the use of any alcohols as additives.
U.S. Pat. Nos. 5,324,335 and 5,465,613 both in the name of the same assignee relate to fuels produced by the Fischer-Tropsch process which also contain inter alia alcohols formed in situ in the process which is recycled to the process. Whilst several primary alcohols are disclosed most of these are linear except the reference to methyl butanol and methyl pentanol. However, the streams recycled contain a considerable amount of other components such as, e.g., aldehydes, ketones, aromatics, olefins, etc. Also, the amount of alcohols generated by this process, especially the content of branched alcohols ( less than 0.5%), appears to be very low in relation to the total stream recycled.
U.S. Pat. No. 5,720,784 refers to fuel blends and the difficulty in rendering diesel fuels miscible with the conventionally used methanol and ethanol. This document purports to mitigate the problem of miscibility by adding to such formulations a C3 (excluding n-propanol)-C22 organic alcohol. However, whilst the document refers to the use of higher alcohols to form single phase compositions which are not prone to separation, it is silent on the nature of the diesel fuelxe2x80x94for these can vary significantly in their composition from light naphtha to heavy duty diesel oilsxe2x80x94nor indeed the effect of any of the alcohols referred to on the problems of particulate emissions when using such fuels in diesel fuel powered internal combustion engines. Furthermore, when addressing the issue of miscibility, it fails to distinguish between fuel compositions which contain the lower C1 and C2 alcohols and compositions which contain no lower alcohols.
WO 92/20761 discloses compositions comprising biodiesel in which the base fuels are predominantly esters and alcohols. There is no mention in this document of reducing particulate matter from emissions.